1. Field
Example embodiments are directed to unit pixels, an image sensor containing unit pixels, and method of fabricating unit pixels, and, more particularly, to unit pixels with improved photosensitivity, an image sensor containing unit pixels with improved photosensitivity, and a method of fabricating unit pixels with improved photosensitivity.
2. Description of the Related Art
Image sensors may be semiconductor elements that convert an optical image into an electrical signal. Image sensors may be categorized into charge coupled devices (CCDs) and complementary metal-oxide-semiconductor (CMOS) image sensors.
A CCD may have a structure in which each MOS capacitor is more closely located and charges are stored in the MOS capacitor and transferred to a target. A CMOS image sensor may employ CMOS technology that uses a control circuit and a signal-processing circuit as peripheral circuits, and may adopt a switching mode that detects outputs sequentially.
Generally, CMOS image sensors may be divided into an active pixel sensor (APS) array and a logic region, which may also be referred to as a peripheral circuit region. The APS array may sense light and generate electrical signals, and the logic region may process electrical signals generated by the APS array. The APS array may include a photoelectric transformation element that senses light and converts the light into electrical signals. An increased surface area of a photoelectric transformation element, such as a photodiode for example, may improve the photosensitivity of an image sensor.
As the integration density of a CMOS image sensor increases, the area of an APS region may be increased to a degree. In response, a microlens may be employed to change the path of light incident on an area other than a photodiode, and the light may be focused onto the photodiode.
However, even with the use of a microlens within an image sensor for condensing light, light incident obliquely onto the microlens may not reach a photoelectric transformation element. Thus, the amount of incident light reaching the photoelectric transformation element may be reduced, and the photosensitivity of the image sensor may be reduced.